1. Technical Field
The present invention relates to a physical quantity sensor, and an electronic device including this physical quantity sensor.
2. Related Art
Recently, an angular velocity sensor capable of detecting an angular velocity has been widely used for a car navigation system, a video camera for attitude control such as correction of movement of the video camera during recording, or for other devices. There is a type of angular velocity sensor which detects an angular velocity around an axis within a plane where an element is disposed.
An angular velocity sensor disclosed in U.S. Patent Application Publication No. 2009/0100930 includes an annular driving mass, an anchor disposed at the center of the driving mass, a substrate to which the anchor is fixed, a pair of first mass units disposed opposed to each other in the X axis direction of the driving mass, a pair of second mass units disposed opposed to each other in the Y axis direction of the driving mass, and detection electrodes disposed on the substrate at positions opposed to the first mass units and the second mass units, respectively, all of which components included in the sensor are provided in the X-Y plane.
The angular velocity sensor having this structure detects an angular velocity produced by rotations of the seesaw-shaped first mass units or second mass units caused when a Coriolis force is generated and given thereto by an angular velocity around the X axis or the Y axis inputted by alternate and repeated rotation of the driving mass around an anchor axis extending in the Z axis direction perpendicular to the X-Y plane.
According to the angular velocity sensor disclosed in U.S. Patent Application Publication No. 2009/0100930, however, a centrifugal force is generated by the rotation of the driving mass and oscillates the seesaw-shaped detection electrodes particularly when the rotation direction changes. This oscillation of the detection electrodes generates an output even when an angular velocity is not inputted.
Therefore, such a physical quantity sensor and an electronic device including the physical quantity sensor have been demanded which can eliminate oscillation of detection electrodes at the time of driving, and avoid at least either the effect of a linear acceleration as a physical quantity producing an output other than the angular velocity, or the effect of an angular velocity around an axis other than the detection axis when the sensor is used as an angular velocity sensor, for example.